The rotary drums currently used in these different fields are habitually of a substantially cylindrical, elongated shape. For support, they rest on cylindrical rollers, generally disposed in pairs to constitute a rolling station directly co-operating with the outer shell of the drum or with roller rings and/or tracks, or strips, provided around the outer shell.
The axes of the rollers are parallel to the main axis of the drum. The rolling stations, hence the rings, are at least two in number: in this case, the drum is isostatically supported. They can also be more numerous, according to the dimensions of the apparatus, and, in particular, the length/diameter ratio. There may thus be three, four or more rolling stations. In this case, the support is ‘hyperstatic’, or statically redundant.
By way of example, the calcining kilns or furnaces used in the cement industry or in the treatment of ores have diameters possibly in excess of 7 m and lengths possibly in excess of 200 m; primary sugar extractors can have a diameter of 9 m or more for a length of 60 m or more.
The rotational movement of the apparatus is most often obtained by means of an annular gear fixed to the outer wall, driven by one or more gear wheels, themselves driven by a motor.
Another known technique, particularly in the sugar industry, consists in driving the apparatus directly through friction between roller and roller ring, one or more rollers being driven via a mechanical or hydraulic transmission system.
The rotary drum is subjected to numerous mechanical stresses, either on account of its movement, and of the weight of the material being processed, or on account of temperature gradients when heat exchange takes place. It is liable, therefore, to become deformed, temporarily or permanently, with the result that its main axis is no longer rectilinear.
One consequence is that the part of its axis located in the area of contact between roller and roller ring is not parallel to the axis of the rollers.
In this case, contact between the rollers and the roller ring is not uniform over the entire width. The stress applied to the roller, and to the roller ring, can then attain locally high values which cause abnormal, irregular wear.
In addition, when the drum is driven in rotation by the roller or rollers, the contact surface may become insufficient to transmit the driving torque.
To avoid this drawback, there are known roller supports enabling the axis of the roller to be held constantly parallel to that of the roller ring. However, in the devices developed to date to obtain this result, the mobility of the roller support is obtained by means of sliding connections.
Such devices thus require maintenance so that sliding can always take place. In addition, the sliding causes wearing of the mechanical components in question, and generates a load moment which opposes the mobility of the support and causes a phenomenon of hysteresis.
The object of the present invention is to provide a support device for a rotary drum, including at least one roller capable of co-operating with the drum, such as to remedy the aforementioned drawbacks and enable the axis of the roller to be held constantly parallel to that of the drum.
Another object of the invention is to provide a support device for a rotary drum in which the number of parts subjected to friction is minimized.
One advantage of the present invention is that it slows down the wearing of the mechanical parts used.
Further objects and advantages of the present invention will emerge in the course of the description that follows, which is given merely by way of illustration and is not intended to limit same.